EVANSTON, Ill., March 14, 2014 — Existing photon number resolving (PNR) detectors are not ideal. They require extreme cooling to ensure accuracy, and often can slow the performance progress in systems such as quantum computers. Northwestern University researchers have come up with a new approach that operates PNR-enabled high-performance imaging systems at short-wave IR (SWIR) wavelengths. This could benefit applications such as scalable quantum computing, noninvasive diffused optical imaging and optical coherence tomography (OCT). A nanoinjection detector, which follows the principles of dim-light detection by rod cells in the human eye, has been developed. SWIR images taken simultaneously with an InGaAs imager are shown above the same images taken with the nanoinjection imager. Images courtesy of SPIE. The researchers note that photons are absorbed over the large volume of the rod cells, but the resulting chemical reactions are channeled toward nanoscale current valves. This process allows quantum efficiency and sensitivity to be simultaneously high, they said. Based on the indium phosphide (InP) material system, the new detector is a layered structure made up of an n-doped InGaAs absorber, a p+-doped gallium arsenide antimonide (GaAsSb) hole trap, an undoped indium aluminum arsenide (InAlAs) etch stop, and an n+-doped InP injector. It is highly scalable, with very low CMOS-compatible operating voltages. Layered nanoinjection detector. The new detector touts high uniformity and nearly bias-insensitive high internal gain characteristics, which makes the device suitable for use with compact, large-format, high-pixel-density imagers. It also has demonstrated a higher signal-to-noise ratio compared with traditional SWIR imagers. Until recently, the most effective SWIR detectors have been transition edge sensor (TES) superconductors and semiconductor avalanche photodiodes (APD), which produce millions of carriers from an electron-hole pair generated by a single photon. The researchers say that the practical application of these is limited, as neither can generate large imaging arrays. Also hindering practical usefulness is the fact that a TES requires extremely low temperatures to operate, and that APDs typically have very large dark count rates. The new nanoinjection detector addresses these obstacles. The research was published in the SPIE journal Optoelectronics & Communications. For more information, visit: www.northwestern.edu.